1. Field of the Invention
The invention relates to the field of ionizers combined with ion-mobility spectrometers (IMS) for the detection of trace amounts of organic compounds in gas and methods of using the same.
2. Description of the Prior Art
Miniature mass spectrometry is a powerful in-situ tool for identifying a wide variety of chemical compounds. For applications that cover many disciplines such as planetary exploration, residual gas analysis, and environmental applications, there is a need for an in-situ analytical separation device or chemical sensor which is rugged, light weight, low power, small, fast, and requires minute quantities of sample for analysis. These requirements are also applicable for the detection of certain organics in the medical sciences (analyzing human breath to detect compounds associated with certain deadly diseases such as lung cancer and cirrhosis of the liver), for a chemical sensor for use on the battlefield (chemical warfare agents), law enforcement (drug interdiction and explosives detection), and food monitoring and control.
Gas chromatography/mass spectrometry (GC/MS) is perhaps the most prominent of current techniques presently available for the analysis of organic compounds. However, conventional GC/MS detectors have three notable shortcomings. First there is limited sensitivity. Commonly used GC/MS detectors likely lack the sensitivity needed to detect organic compounds at the sub parts-per-billion (ppb) level, a necessity that should be a requirement for in-situ chemical analysis. Second, the fragmentation of large organic species prevents accurate identification of organic samples. When a mixture of organic components is to be analyzed, the complexity of breakup patterns puts very severe constraints on the quantitative analysis of the concentrations of these components. Third, strenuous vacuum requirements. In conventional GC/MS systems require a high vacuum environment which greatly increases the size, weight and mechanical complexity. A new detector that will circumvent these problems (i.e. a detector which does not need a complicated vacuum system to operate, has detection sensitivity at levels below parts per-billion and is free from any fragmentation problem) is needed.
The invention is an apparatus which combines a novel high-pressure (xcx9c1-5 Torr) hollowcathode ionizer and an ion-mobility-spectrometer (IMS) for the detection of trace amounts of organic compounds. The detector uses a novel xe2x80x9csoft-ionization techniquexe2x80x9d, based on a proton-transfer reaction involving H3O+, to efficiently ionize (e.g.  greater than 95%) most large molecules without fragmentation. This is critical for the unambiguous identification of species. In addition, H3O+ ions do not react with clean air. The result is that the normal components of air (O2, N2, CO2, CO, and the like) pass through the detector and do not get detected with the spectra of most organic compounds.The advantages of this approach in comparison to commonly used gas chromatography/mass spectrometry (GC/MS) is extremely low background signal owing to the inherent filtering capabilities of our novel H3O+ ionization technique, increased sensitivity, no fragmentation of large organic species, and no high vacuum requirements. The unit can operate under atmospheric conditions. In addition, the cost of this unit is at the time of filing expected to be in the range of $3-6000, which is much less than typical GC/MS units. Finally, the instrumentation is relatively small. For example a laptop computer used to acquire the data is larger than the instrumentation and supporting electronics. Applications of the invention to the fields of: (1) medicine as a breath analyzer for detection of lung cancer, diabetes, liver cirrhosis, etc., (2) law enforcement in drug interdiction and explosives detection, (3) food monitoring and control, (4) environmental monitoring and (5) space applications such as searching chemical signatures of life on outer planets are expected to be substantial and only a very partial list were utility can be found.
While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of xe2x80x9cmeansxe2x80x9d or xe2x80x9cstepsxe2x80x9d limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals.